Cook potatoes in salted water for 20 mins until tender. Preheat oven to 200ºC. Cut white bulbs off the spring onions and roughly chop. Finely slice the green tops and set aside. Spread fish chunks on baking tray and scatter over the chopped spring onions. Drizzle with 2 tablespoons olive oil, sprinkle with salt and pepper and roast for 6 mins. Drain off liquid and put fish into a 2.5 litre/4 pint ovenproof dish. Drain potatoes well, add milk and egg and mash. Melt butter in a small pan and cook spring onion tops for 1 minute. Add tumeric and stir for 30 seconds and then add to mashed potato and beat well. Add salt and pepper to taste. Heat remaining olive oil in a large frying pan, add courgettes and fry for 5 mins. Add cardamom pods and fry for 30 secs. Stir in tomato sauce, bring to boil and simmer for 1 min. Season, remove from heat and cool. Pour sauce over fish and spring onions and spoon over mash so all sauce and fish are covered. Rough up with fork. Cool, keep covered in fridge. Uncover pie and bake for 35-40 mins.